Crystal growth method

ABSTRACT

In the CZ process using a cooling member surrounding a single crystal, the cooling member is permitted to effectively serve to increase a pulling speed. Cracks of the single crystal due to excessive cooling are prevented to occur. A high crystal quality is acquired. In order to realize these objects, the temperature of the inner peripheral surface of the cooling member  6  opposing to the outer peripheral surface of the single crystal  4  is restricted to 500° C. or below, even in the lower end, the temperature of which becomes the highest. To achieve this restriction, the thickness T of the cooling member  5  is 10 to 50 mm. The height H of the cooling member  6  is 0.1 to 1.5 times the diameter D of the single crystal  4.

TECHNICAL FIELD

[0001] The present invention relates to a crystal growing process usedfor manufacture of a silicon single crystal or the like utilized as asemiconductor material.

BACKGROUND ART

[0002] A variety of methods are available for manufacturing siliconsingle crystals, of which the Czochralski process (the CZ process) istypical. In producing a silicon single crystal by the CZ process, as iswell known, a seed is immersed in a silicon melt formed in a quartzcrucible. The seed is gradually pulled up to allow a silicon singlecrystal to grow beneath the seed while rotating the crucible and theseed.

[0003] In pulling up a silicon single crystal by means of the CZprocess, it is known that the defect distribution etc. in the crystalcross section are governed by the rate of crystal growth, therefore thepulling speed. More specifically, as the pulling speed is increased, aring-shaped OSF generation zone is moved towards the periphery and isfinally excluded to the outside of the effective portion of the crystal.Conversely, a decrease in the pulling speed drifts a ring-shaped OSFgeneration zone towards the central part of the crystal, and eventuallythe zone disappears in the central part.

[0004] While both the outside and inside of an OSF generation zone aredefect generation zones, their kinds of defects are different. Inaddition, it is known that a significant increase of the pulling speed,as a matter of course, improves productivity while refining the defects.Consequently, a speed-up in the pulling has been pursued as an approachto growing crystals.

[0005] Provision of a heat shield is known as a technique for high speedpulling. A heat shield is a cylindrical heat shielding member in a shapeof inverted truncated cone that is disposed surrounding the singlecrystal. The shield is provided to speed up the pulling by shielding theradiation heat primarily from the melt in the crucible and heatersplaced outside the crucible to facilitate cooling of the single crystalto be pulled up from the melt.

[0006] Furthermore, attention is recently given to a technique where acylindrical cooling member that is forcibly cooled by water is placedinside the heat shield (Japanese Patent Laid-Open Nos. 63-256593,8-239291, 11-92272 and 11-292684) Installation of a cylindrical coolingmember that is forcibly cooled by water inside the heat shieldsurrounding the single crystal facilitates cooling of the singlecrystal, particularly the high temperature portion thereof, leading to afurther speedup of the pulling.

[0007] However, it has turned out that the conventional crystal growingprocess using a cooling member does not always permit the cooling memberto effectively increase the pulling speed and also causes the problemsto be described below with regard to the quality of the single crystaland the safety of operation.

[0008] A copper-based metal member forcibly cooled by water passage isfrequently used as a cooling member from the viewpoint of coolingcapacity and cost efficiency for the single crystal. Providing simplysuch a cooling member does not serve to increase the pulling speed inmany cases. When the cooling member does not effectively act for aspeedup of the pulling, the diffusion of heavy metals such as Fe and Cuis facilitated leading to contamination of the single crystal startingfrom its periphery, because the portion of the single crystal with ahigh temperature of 1300° C. or above is elongated and the time in whichthe single crystal passes through an area of a high temperature of 1300°C. or above is increased as well.

[0009] Speed up of the pulling requires cooling of the portion of thesingle crystal with a high temperature of 1300° C. or above by a coolingmember and its increased cooling capacity causes the risk of rapidcooling of the portion of 1300° C. or below also. The rapid cooling ofthe portion of 1300° C. or below also causes rapid deformation of thecrystal caused by the cooling in dislocation of the crystal being pulledup. As a result, a residual stress is generated because of thedifference of extent of the deformation in the boundary between thenon-dislocated and dislocated portions, leading to the likely generationof cracks in cooling of the crystal drawing or after the pulling. Whenthis crack is generated, the cooling member may be broken in some cases,leading to disasters including a steam explosion.

[0010] The object of the present invention to provide a crystal growingprocess that can make the cooling member effectively serve to increasepulling speed and also effectively prevent cracks caused by excessivecooling of the single crystal, in pulling the single crystal by the CZprocess using a cooling member.

DISCLOSURE OF THE INVENTION

[0011] In order to achieve the above described object, the inventorsfocused attention on the dimensions of the cooling member and thesurface temperature and have investigated in detail the relationsbetween the high speed pulling and these factors. As a result, thefollowing facts have been found.

[0012] When the thickness of the cooling member is less than 10 mm, thetemperature of the cooling member is extremely increased because of theradiation from the single crystal, which in turn reduces the coolingefficiency for the crystal, leading to the difficulty in the realizationof a high speed pulling. On the other hand, when the thickness exceeds50 mm, not only the cooling efficiency stops increasing, but also thefield of the view of a camera used for controlling the crystal diameteris restricted, and the flow of gases such as Ar that is flowed throughthe furnace is reduced leading to dislocation due to the precipitationof SiO.

[0013] When a portion with a temperature exceeding 500° C. exists in theinner peripheral surface of the cooling member opposing to the outerperipheral surface of the single crystal to be pulled from the melt, thecooling efficiency for the crystal is dramatically reduced, leading tothe unrealization of a high speed pulling.

[0014] When the height of the cooling member is less than 0.1 times thediameter of the crystal, the portion of the single crystal with a hightemperature of 1300° C. or above cannot be cooled efficiently. However,when its height exceeds 1.5 times the diameter of the crystal, theportion with a temperature of 1300° C. or below is rapidly cooled, andwhen a dislocation is formed in the single crystal, cracks are likely tobe generated.

[0015] When the distance from the lowest end of the cooling member tothe melt exceeds 100 mm, the effect of cooling of the portion of thesingle crystal with a high temperature of 1300° C. or above issignificantly reduced, thereby making a speedup in the pullingdifficult. On the other hand, when the distance is shorter than 10 mm,the risk of contact of the cooling member with the melt is increased.Further, the temperature of the melt close to the cooling member quicklydecreases, causing the problem of the pulled crystal being likely todeform due to a decrease in the radial temperature gradient of the melt.

[0016] When the emissivity of the inner peripheral surface of thecooling member is less than 0.7, the effect of cooling of the portion ofthe single crystal with a high temperature of 1300° C. or above isreduced, leading to a difficulty in speedup of the pulling.

[0017] When the flow rate of the cooling water supplied to the coolingmember is less than 1.5 L/min, the temperature of the cooling member isincreased, and therefore the crystal cannot be cooled effectively. Whenthe flow rate exceeds 30 L/min, the effect of cooling of the crystalstops increasing, resulting in a waste of the cooling water.

[0018] The crystal growing process of the present invention is made inview of the above described findings and permits the cooling member toeffectively serve to increase the pulling speed, while effectivelypreventing cracks caused by excessive cooling of the single crystal, byutilizing a cooling member with a height 1.5 times or less the diameterof the above described single crystal and also by keeping 500° C. orbelow the temperature of the inner peripheral surface of the coolingmember opposing to the outer peripheral surface of the single crystal,when crystal growing is carried out by utilizing a furnace equipped witha ring-shaped cooling member disposed surrounding the single crystalgrown from a raw material melt by the CZ process.

[0019] The lower limit of the height of the cooling member is preferably0.1 times or more the diameter of the single crystal, from the viewpointof a speed-up in the pulling. The particularly preferable height is 0.25to 1.0 times the diameter of the single crystal.

[0020] The temperature of the inner peripheral surface of the coolingmember is not specified in particular, because the lower it is, thebetter. The particularly preferable surface temperature is 200° C. orbelow.

[0021] For other factors than the height of the cooling member and thetemperature of the inner peripheral surface, the thickness of thecooling member is preferably from 10 to 50 mm. Additionally, the flowrate of the cooling water to be supplied to the cooling member ispreferably from 1.5 to 30 L/min. In addition, the distance from thelower end of the cooling member to the melt surface is preferably from10 to 100 mm. Furthermore, the emissivity of the inner peripheralsurface of the cooling member is preferably not less than 0.7.

[0022] The cooling member is made of a metal material which is forciblycooled by water passage. The primary component of the metal ispreferably copper, which exhibits good heat conduction and isinexpensive. When the cooling member is composed of a copper-basedmetal, blacking by plating with black Cr metal or oxidation is effectiveas a method of increasing the emissivity of the inner peripheralsurface. In particular, plating with black Cr metal also has the effectof protecting soft copper-based metal to suppress contamination by thecrystal of copper.

[0023] In general, the pressure of the atmosphere inside the furnace isnot more than 13300 Pa, and so heat transfer by the gas can be neglectedand the heat removal from the pulled crystal is exclusively by heatradiation. In the crystal growing process of the present invention theheight of the cooling member and the surface temperature are specifiedfrom this viewpoint, and the distance from the crystal surface to thecooling member is not particularly specified because heat transfer bythe gas can be neglected.

[0024] It is advisable that the cooling member be combined with a heatshield and placed inside of it. Combination with a heat shield not onlyfacilitates the cooling of the crystal, but also effectively constrainsa rise in the temperature of the cooling member itself, therebyincreasing the pulling speed.

BRIEF DESCRIPTION OF THE DRAWING

[0025]FIG. 1 shows a schematic block diagram of the inside of a furnacesuitable for carrying out the crystal growing process of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0026] Referring to FIG. 1, an embodiment of the present invention willbe described below.

[0027] The furnace is equipped with a main chamber and a pull chamber asthe puller body. A crucible 1 is placed in the center of the mainchamber. The crucible 1 is composed of an inner quartz crucible whereinpolycrystalline silicon is loaded, and an outer supporting crucible madeof graphite. This crucible 1 is driven rotated and elevated on asupporting axis called a pedestal.

[0028] Outside the crucible 1 is concentrically placed a resistanceheater and in the farther outside of the heater is placed a thermalinsulating tube along the inner surface of the main chamber. The heatermelts polycrystalline silicon charged filled in the crucible 1 and formsa melt 2 of silicon in the crucible 1.

[0029] On the other hand, above the crucible 1 is hung a wire 3 as apulling axis through the center of the pull chamber. The wire 3 isdriven to be rotated or elevated in the axial direction by a pullingmechanism provided in the upper part of the pull chamber. In the lowerend of the wire 3 is fixed a seed chuck holding a seed. A seed held bythe seed chuck is immersed in the melt 2 in the crucible 1 and a siliconsingle crystal 4 is grown beneath the seed by driving the wire 3 toslowly lift the seed while rotating it.

[0030] Above the crucible 1 is also concentrically placed a cylindricalheat shield 5 surrounding the single crystal 4, close to the melt 2 ofthe crucible 1. The heat shield 5 is made of graphite and its diametergradually increases from the lower part upwards in order to effectivelyshield the radiation heat from the melt 2 in the crucible 1, with thelower part of the shield inserted into the crucible 1 and the shieldlocated above the melt 2 in the crucible 1.

[0031] Inside the heat shield 5 is concentrically installed acylindrical cooling member 6. The cooling member 6 is composed of acopper-based metal of good heat conduction and is cooled forcibly bycooling water flowing through the inside of the object. This coolingmember 6 is placed inside the lower part of the heat shield 6 andfacilitates the cooling of its high temperature portion by surroundingthe single crystal 4, particularly the high temperature portionimmediately after the solidification. In addition, the cooling member 6,as the heat shield 5, is also of tapered shape wherein its diametergradually increases from the lower part upwards.

[0032] Here, the height H of the cooling member 6 is selected to be inthe range of 0.1 to 1.5 times the diameter D of the single crystal 4 andin this case the height is selected to be the same as D. The thickness Tof the cooling member 6 is selected in range of the 10 to 50 mm and inthis case 40 mm is selected. The distance L from the lower end of thecooling member 6 to the melt 2 is selected in the range of 10 to 100 mmand in this case 30 mm is selected.

[0033] In addition, the inner peripheral surface of the cooling member 6is treated by oxidation so that the emissivity of the surface is notless than 0.7, and in this case the emissivity is 0.9. The temperatureof the inner peripheral surface is adjusted so that even the lower endportion, which has the highest temperature, does not exceed 500° C., andin this case a temperature of 30° C. has been realized as thetemperature of the lower end portion by adjusting to the range of 1.5 to30 L/min the flow rate of the cooling water that is supplied by thecooling member 6.

[0034] Now, operational examples will be described of crystal growth bythe above described furnace.

[0035] A raw material of 100 kg of polycrystalline silicon is charged inthe crucible 1 and then the inside of the chamber is made to be an Aratmosphere of 1330 Pa. The raw material of polycrystalline silicon inthe crucible 1 is melted via the heater placed in the outside of thecrucible 1, and using a seed of 100 orientation a single crystal with adiameter of 200 mm is made to grow beneath the seed.

[0036] In this operation, the crucible 1 is gradually lifted, takinginto account the crystal growth, in such a way that the surface level ofthe melt 2 in the crucible 1 is kept constant. In addition, the crucible1 is rotated in the direction opposite to or in the same direction asthe rotational direction of the single crystal 4.

[0037] Since the height H of the cooling member 6, which is in the rangeof 0.1 to 1.5 times the diameter D of the single crystal 4, was selectedto be the same as D (200 mm), and the temperature of the innerperipheral surface of the cooling member 6 in its lower end portion,wherein the temperature becomes the highest, was adjusted to 30° C., aspeed of 2.5 mm/min was attained as the average pulling speed at thecylindrical part of the single crystal.

[0038] Pulling of this single crystal was conducted 5 times and nocracks were produced. The number of LPDs of the wafer with 0.09 μm ormore sampled from the single crystal was not more than 300/wf and thenumber of LPDs with 0.13 μm or more was not more than 10/wf. The Feconcentration was not more than 1×10¹⁰/cm³.

[0039] Similar pulling was carried out with various values of thethickness T and the height H of the cooling member 6. The pullingconditions are given in Table 1 and the results in Table 2. Theoperational example 1 shows the results of the above described operationand the average pulling speed is 2.5 mm/min. TABLE 1 Distance fromAverage Height the lower end of Lower end thickness of cooling membertemperature of cooling cooling to the melt of cooling member membersurface member #1 (Example of 40 mm 200 mm 30 mm  30° C. the presentinvention) #2 (Example of 10 mm 200 mm 30 mm 400° C. the presentinvention) #3 (Comparative  5 mm 200 mm 30 mm 550° C. Example) #4(Comparative 40 mm 400 mm 30 mm  30° C. Example)

[0040] TABLE 2 LPD of not LPD of not Generation Average less than lessthan Fe rate of speed 0.09 μm 0.13 μm concentration crack #1 (Example of2.5 mm/min  300/wf 10/wf   1 × 10¹⁰/cm³ 0 in 5 the present or less orless or less invention) #2 (Example of   2 mm/min  400/wf 12/wf   1 ×10¹⁰/cm³ 0 in 5 the present or less or less or less invention) #3(Comparative 1.3 mm/min 1500/wf 50/wf   5 × 10¹¹/cm³ 0 in 5 Example) orless or less or less #4 (Comparative 2.5 mm/min  300/wf 12/wf 1.2 ×10¹⁰/cm³ 4 in 5 Example) or less or less or less

[0041] As in the operational example 1, in an operational example 2, thethickness of the cooling member 6 was reduced from 40 mm to 10 mm. As aresult, the inner peripheral surface temperature of the lower end of thecooling member 6 was increased from 30° C. to 400° C. Although theaverage pulling speed was reduced to 2 mm/min, it is still a high level.Both the number of LPDs and the Fe concentration were still in a lowlevel and no crack was generated.

[0042] For an operational example 3, the thickness of the cooling member6 was reduced to 5 mm. As a consequence, the inner peripheral surfacetemperature of the lower end of the cooling member 6 exceeded 500° C.and rose to 550° C. The average pulling speed was decreased to 1.3mm/min. No crack was produced, while the number of LPDs and the Feconcentration were remarkably increased.

[0043] In an operational example 4, the height of the cooling member 6was increased from 200 mm to 400 mm, which exceeds 1.5 times thediameter D of the single crystal 4. The thickness of the cooling member6 was kept 40 mm; the inner peripheral surface temperature of the lowerend of the cooling member 6 was 30° C. An average pulling speed of 2.5mm/min was acquired and both the number of LPDs and the Fe concentrationwere relatively low, and cracks were generated in four out of fivesingle crystals.

[0044] As is seen from these results, for the purpose of permitting thecooling member 6 to effectively function for a speed up in the pulling,the control of the inner peripheral surface temperature of the coolingmember 6 is primarily important, and secondly the thickness, whichgreatly affects the inner peripheral surface temperature, is animportant factor. These are also important from the viewpoint ofensuring the crystal quality. In addition, for the prevention of crackscaused by excessive cooling of the single crystal 4, the height of thecooling member 6 is especially an important factor.

[0045] In this regard, when a cooling member is not used, the averagepulling speed is 1.0 mm/min, the number of LPDs of not less than 0.09 μmis not more than 2000/wf, the number of LPDs of not less than 0.13 μm isnot more than 100/wf, and the Fe concentration is not more than1×10¹²/cm³.

[0046] In addition to these operational examples, in the operationalexample 1, the crystal was pulled up after addition of nitrogen orcarbon to the melt; as a result, the number of LPDs of not less than0.09 μm was greatly reduced. Consequently, it has been turned out thatthe addition of nitrogen or carbon to the melt in the crystal growingprocess of the present invention accelerates fining of LPD to proceed.

[0047] In addition, in the operational example 1, when the pulling speedwas reduced in half to 1.25 mm/min and the pulling was conducted underthe condition of the ring-shaped OSF generation zone almost vanishing inthe center of the crystal, the number of LPDs of not less than 0.09 μmwas greatly reduced to 100/wafer. Consequently, it has been found outthat the speedup is possible for crystals that are conventionally pulledup at a speed of 1 mm/min or lower, used for the low LPD wafer chargingmonitor, and that the present invention is effective in a low-speedpulling for the low LPD wafer charging monitor as well.

[0048] Industrial Applicability

[0049] As has been explained thus far, in the rotational pulling usingof a cooling member, the crystal growing process of the presentinvention permits the cooling member to effectively serve to increase apulling speed and also can effectively prevent the cracks due to theexcessive cooling of the single crystal, by controlling the innerperipheral surface temperature and the height of the cooling member.Furthermore, a high quality of the crystal can be ensured as well.Hence, the process is suitable for economical manufacture of a singlecrystal with high quality.

1. A crystal growing process characterized in that when carrying outcrystal growth using a furnace equipped with a ring-shaped coolingmember placed so as to surround a single crystal grown from a rawmaterial melt by means of the Czochralski process, a cooling member witha height being not more than 1.5 times the diameter of said singlecrystal is used, and the temperature of the inner peripheral surface ofa cooling member opposing to the outer peripheral surface of said singlecrystal is not more than 500° C.
 2. The crystal growing processaccording to claim 1, characterized in that the thickness of saidcooling member is from 10 to 50 mm.
 3. The crystal growing processaccording to claim 1, characterized in that the flow rate of the coolingwater to be supplied to said cooling member is from 1.5 to 30 L/min. 4.The crystal growing process according to claim 1, characterized in thatthe distance from the lower end of said cooling member to the meltsurface is from 10 to 100 mm.
 5. The crystal growing process accordingto claim 1, characterized in that the emissivity of the inner peripheralsurface of said cooling member is not less than 0.7.